In molding plastic and rubber materials in molds, release agents are often applied to the internal surface of molds in order to facilitate removal of molded parts from the molds. Typical release agents include metallic soap solutions, silicone-based release agents, tetrafluoroethylene resins and the like. Although metallic soaps, silicone oil and silicone grease exhibit good release properties, these release agents migrate to molded parts. As a result, the surface of molded parts becomes repellent, losing their abilities of uniform coating and subsequent fabrication. The lack of retention requires that the release agent be applied every several shots. On the other hand, the tetrafluoroethylene resins are satisfactory in the retention of release properties and the readiness of molded parts for subsequent fabrication. However, the step of forming a tetrafluoroethylene coating on the mold surface involves high-temperature baking and requires a skill. The use of tetrafluoroethylene resins is thus inadequate as the general mold release treatment.
A number of film-forming silicones are known as disclosed in JP-B 63-060071, JP-B 3-11248 and JP-B 2-9069, all corresponding to U.S. Pat. No. 4,678,688. Cured films of these silicones exhibit insufficient release properties, especially when silicone rubber of the heat-cure type is molded at 180-200° C. and removed. Polymers of perfluoroalkyl silazanes are also known as disclosed in JP-A 2-49082 corresponding to U.S. Pat. No. 4,678,688. Polysilazane films also have unsatisfactory release effects and lack durability because they become hard and brittle.